(2R)-2-(1,3-Dioxoisoindolin-2-yl)-4-(methylsulfanyl)butanoic acid

The title compound, C13H13NO4S, the 1,3-dioxoisoindolin-2-yl unit is planar (r.m.s. deviation 0.0192 Å) and is oriented at a dihedral angle of 79.14 (18)° to the carboxylate group. An intramolecular C—H⋯O hydrogen bond leads to the formation of a planar (r.m.s. deviation 0.0419 Å)R(5) ring motif. In the crystal, molecules are connected through O—H⋯O and C—H⋯O hydrogen bonds with R 2 2(9) ring motifs into chains extending along the b axis.

The title compound, C 13 H 13 NO 4 S, the 1,3-dioxoisoindolin-2-yl unit is planar (r.m.s. deviation 0.0192 Å ) and is oriented at a dihedral angle of 79.14 (18) to the carboxylate group. An intramolecular C-HÁ Á ÁO hydrogen bond leads to the formation of a planar (r.m.s. deviation 0.0419 Å )R(5) ring motif. In the crystal, molecules are connected through O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds with R 2 2 (9) ring motifs into chains extending along the b axis.

Comment
Isocoumarin and 3,4-dihydroisocoumarin have shown an impressive array of biological activities such as anti-tumor (Hill et al., 1986), anti-leucemic (Canedo et al., 1997 and anti-microbial (Whyte et al., 1996). The titled compound (I, Fig. 1) is an intermediate towards the synthesis of chiral isocoumarin. The biological activity of the title compound and synthesis of its complexes are in progress.

Experimental
The methionine (2.0 g, 13.4 mmol) and phthalic anhydride (2.13 g, 14.38 mmol) were added to a flask with constant stirring at 423 K for 2 h. The reaction mixture was brought to room temperature and the crystalline phthallic anhydride on the walls of the flask were removed. The solid crude product was purified by crystallization from ethanol/water (7:3) that afforded colorless prisms of the title compound (I).

Refinement
All the Friedal pairs were merged.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.